EGF receptor and other members of the ErbB family of receptor tyrosine kinases (RTKs) play essential physiological roles in development and maintenance of epithelial tissues by generating cell proliferation, survival, differentiation, and migration signals in response to specific ligands. Activation of ErbB receptors is also linked to the initiation and progression of human cancers. These RTKs have emerged as important therapeutic targets of anti-receptor antibodies and kinase inhibitors, although both therapeutic modalities suffer from rapid resistance development, necessitating alternate approaches to ErbB-targeted therapy. An essential pre-requisite for cellular response to EGFR and other RTK ligands is that an activation-competent pool of RTKs must be displayed on the cell surface. ErbB receptor overexpression increases this activation-ready pool. Sufficiently high levels of ErbB receptor overexpression induce ligand-independent activation, which can also be achieved by cancer-associated activating mutations. A fundamental feature of RTK function is that the newly synthesized as well as ligand-internalized receptors undergo a sorting process that determines whether they will recycle back to the cell surface for ligand binding and signaling or will be targeted for lysosomal degradation. We, and others, have shown that Cbl family of ubiquitin ligases are essential regulators of the lysosomal fate. Studies carried out by others and by us during the current funding period have led to a novel hypothesis that members of the C-terminal Eps15-homology (EH) domain-containing (EHD) protein family function as key regulators of the recycling fate of receptors. In this competing renewal application, we will employ unique EHD knockout mouse models and cellular reagents derived from these animals together with a vast array of immunological, biochemical and cellular reagents that have been generated to test the hypotheses: EHD protein-dependent endocytic recycling is a key controller of the cell surface display and recycling fate of EGFR; loss of EHD function will attenuate the ability of EGFR to propagate oncogenic signals in vitro and will abrogate EGFR-driven oncogenesis in vivo; and abrogation of endocytic recycling will enhance the efficacy of EGFR targeted therapy with an inhibitory antibody. Thus, this proposal will evaluate the endocytic recycling of EGFR as a novel therapeutic target in EGFR-driven cancer. Insights gained from these studies should further our understanding of the molecular and cell biological regulators of oncogenic signaling by RTKs, and help validate the endocytic recycling of RTKs as a new approach to rationally design anti-cancer agents to potentiate existing RTK-targeted therapies.